Can’t transfer pictures from iPhone to computer using dcim folders

Why can I not transfer my pictures from DC I am folder‘s? It says no room or copy air which there’s plenty of room on my external drive. Good morning and all the iCloud folders have pictures mixed up and Apple folders from long time ago to current this is very aggravatingI use my phone for a lot of pictures and you need to transfer them to my external drive without a lot of issues and duplicates